Using industrial process controls is going to make it needlessly expensive. Much easier would be to use plain old thermistors, and roll your own control and interface with a small embedded controller. See the 8051 cores from Atmel and Maxim/Dallas! There are controllers with ADC's onboard, and if you need more, use a controller with onboard I2C instead, and put all your input and output peripherals on I2C. Use a transistor and relay for switching.

For probes there are already lots of good sensors that come as parts of cars already. Transmission and axle temp sensors can go into the drain plugs. It's difficult to get accurate engine oil temp. I would prefer to have this at the oil pump, and the probe must be in the flow, this is usually hard but we have oil coolers with hoses.

So what to do about active cooling? Sure if you have an automatic transmission an electric fan in front of the radiator will help. With everything else, you can't do much about it. People usually replace their axle housings for ones which hold more oil and have big cooling fins, if they get warm.

I think you can feel it when your brakes get too hot. Also it might not be the temperature of your brake rotors that is causing the malfunction, but of the brake fluid.

We are getting off topic for the board!